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Fitting the Cowl - How good is good enough?

UnPossible

Well Known Member
Well, I've waited a few days, and the cowl fairy has not flown in to fit my cowl :(... guess it's time to get busy.

I've spent a couple of hours trimming the cowl around the spinner area. It's getting closer, but it's not perfect.

Below are a couple of pics of my progress... It looks like in order to get a good circle behind the spinner, I will need to fill in a bit of the joggle on either side of the spinner.

I'm wondering how good is good enough here to drill the one hole on each side where the cowl halves overlap, and move forward to fitting it on the fuselage?


i-dmVs9kk-XL.jpg


i-zgjnkWg-XL.jpg
 
Do you have the openings sized vertically like the plans (IIRC) call for? Is the round area behind the spinner a true circle? Have you adjusted the flanges to the best of your ability to make the transitions at the front of your cowl smooth? If so, the rest is sandpaper, micro, and reinforcements (as necessary) which means you're ready to move forward.

The one thing I will tell anyone is that (generally) 30 more minutes of alignment/fitting up front will save far more than that in finishing work.

As far as the joggle goes, I had to fill those and also had to use filler at the outside joint on the cowl inlets - either on the top or bottom, I don't remember.
 
You may also want to anticipate enough gap for your paint job otherwise you could have edges rubbing after painting. Also, paint will adhere to a rounded edges far better then sharp edges.
 
take time

I read many posts that recommended spending a lot of time here to make it right. That's pretty much what I did. Yes, it took about 10x more time than I thought it would, and of course now with experience I could do it faster.

It helped me when someone reminded me that you can add "meat" behind as well, and sand down the front to get it to fit right. It's a very iterative process.
 
I'm wondering how good is good enough here...

I just finished this fitting. Started with two halves in about the same shape it looks like yours are in (close but not perfect). Found that it does make a difference in final fitment! Getting that joggle at spinner hole to fit well was more important than I anticipated. Make sure you grind out inside corners of that joggle well and any high spots on front of top cowl so that they lay flat when joined and that the gap between the two is almost zero (you can sand out for paint gap later). Also make sure that the outside corners of your air inlets are not hitting high spots. That created some issues for me as well. These two parts should "fit like a glove" when your done.

Overall, it took WAY more time here than I thought. The better you make this section fit, the better off you will be when fitting to fuse. Be patient and "sneak up on it" (taking a little off at a time) and you'll be glad you did.
 
Well after messing around for quite a bit this evening, I have the two cowl halves fitting together pretty well.


i-rdzKwGh-XL.jpg


My only question/concern is that if I measure the height of each opening at the middle of the opening, one measures a bit over 4-1/2" and the other measures a bit under 4-3/4". It is not noticeable, but wondering if I should try and bring down the taller one to match the shorter opening height? Any thoughts before I plow ahead in the morning?
 
My original inlets weren?t even close to the same shape and size, you couldn?t ever tell by looking at it though. I wouldn?t bother trying to make them the exact same shape and size.
I would check to make sure the opening diverges and gets larger as it moves the couple inches aft toward the baffling, you don?t want it to ?neck? down and get smaller.
 
My only question/concern is that if I measure the height of each opening at the middle of the opening, one measures a bit over 4-1/2" and the other measures a bit under 4-3/4". It is not noticeable...

I am always reminded of a 1950's quote from Dear Abby...

Any girl can get married if she sets her sights low enough.

Go for the absolute best you can. You're going to be looking at this thing for a long time, and your name will be on the data plate long after you're dead.
 
I'm with Dan. I hate to say it, but you still have a ways to go. When I fit mine, I added a joggle to the lower cowl around all the vertical sides in the very front to help seal the gap and to help with alignment.

IMG-2344.jpg
 
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